The Solution Conformation of Lactal and ITS Hexa-O-Acetyl Derivative

Abstract

The conformation of lactal (1) in D₂O and DMSO-d₆ has been investigated by employing NMR techniques and molecular mechanics calculations. The glucal ring shows a ⁴ H₅ conformation in deuterium oxide and DMSO-d₆. In contrast, the glucal ring of the hexa-O-acetyl derivative (2) in CDCl₃ can be described as an equilibrium between the ⁴ H₅ and ⁴ H₅ forms. The disaccharide 1 has a restricted flexibility with the Φ angle oscillating about -105 ± 30° and the Ψ angle varying about -145 ± 30°. Compound 2 shows a similar conformational behaviour.